Danielle Sade B.Sc., CAHP
When exposed to airborne essential oils, an aromatic paradigm occurs. This paradigm results in the formation of feelings and thoughts, and also results in an experience that creates a personal perception of reality. At the same time, it influences the internal landscape with a biological cascade of events in which the olfactory system, the neuroendocrine and autonomic nervous systems are involved.
Let’s begin with the olfactory system that forms our sense of smell. The olfactory system mediates our chemical sense of smell and taste, and it signals to us when we are in danger and provides us with pleasure and well-being. When we are exposed to odor compounds, it influences the neuroendocrine system, neurotransmitters, neuromodulators, and the psychological and physiological pathways, which, are not fully understood. This gives us indication that our sense of smell goes beyond just a scent experience and that physiological pathways influence changes in different variety of hormones such as cortisol, DHEA, estradiol, dopamine and stress biomarkers 
Information from the olfactory is processed in the limbic system where we find the amygdala-the home of the emotions, and the hypothalamus—the control center in the brain that is responsible for signaling to the pituitary gland (the master gland of the endocrine system).
Which leads me to bring to your attention the Hypothalamus Pituitary Axis’ (HPA) response to stress. This dynamic system is triggered by the amygdala (the area in the brain that processes emotions). When the amygdala detects stress, it sends signals to the Hypothalamus, which then activates the Sympathetic nervous system (Fight or Flight). The hypothalamus then cues the neuroendocrine neurons to release the corticotropin-releasing hormone CRH, which acts on the pituitary gland to stimulate the production and release of adrenocorticotropic hormone CTH. This, in turn, initiates the adrenal glands to secrete cortisol and corticosterone that influences the physiological homeostasis.
When the HPA is constantly active due to stressful events or feelings, it will eventually affect the body and contribute to illnesses that are associated with the endocrine system, such as Diabetes, Thyroid imbalances, Reproductive disorders, and Insomnia and many studies prove that aromatherapy interventions can help to recruits the Parasympathetic State. (Rest, Digest and Repair)
The human body is in a continuous need to be in a homeostatic state. The fundamental role of the endocrine system is to ensure intercellular communication, coordination, and control, for achieving homeostasis in the body.
In summary, the Olfactory System, the Autonomic Nervous system, and the Neuroendocrine system regularly interact with one another to produce a paradigm response that involves the whole body! With this understanding, the therapeutic approach helps to shift the paradigm with the influence of Aromatherapy–via the olfactory system to recruit a parasympathetic state. The administration of some essential oils with inhalation methods can help withdraw the sympathetic state.
Aromatherapy can be used as a method of treatment that provides comfort and well-being to reach a paradigm that helps the individual shift the way they feel inside out.
As an Aromatherapist, the objective is to use an integrative approach to improve the quality of sleep and reduce physical/emotional stress and Anxiety by slowing down the HPA and recruiting the parasympathetic state with relaxing essential oils. The following oils have demonstrated their influence on the autonomic nervous system and their capacity to help support the homeostasis of the body.
Bergamot Citrus Bergamia - Studies have demonstrated that the essential oil vaporized and inhaled can significantly reduce the cortisol levels via the olfactory bulb. It also has a time released effect as the constituents find their way through the respiratory tract and are then transported to the nervous system via blood circulation, thus recruiting the parasympathetic state. (Wantabe et al., 2015) Neroli Citrus Aurantium - It was found that Inhalation of Neroli reduces blood pressure and the cortisol levels by having a calming effect on the nervous system. (Choi 2014)  Clary Sage Salvia sclera - Short periods (1-5 minutes) of inhalation of clary sage essential oil administrated to a group of menopausal women in depressed states resulted in a significant reduction of the cortisol levels in blood plasma. (Lyung Bok Lee et al., 2014) 
Australian Sandalwood Santalum austrocaledonicum - Alpha-Santalol found in Australian Sandalwood was able to permeate into the skin and lower blood pressure. (Heuberger E et .al.)
Rose Otto Rosa damascene - Studies on 43 healthy individuals have demonstrated that through inhalation of Rose Otto, there was a reduction in the sympathetic activity and also in the levels of adrenalin were decreased.  Inhalation of Rose Otto inhibited cortisol due to chronic stress through inhibiting HPA. (Fukada et al., 2011)
Patchouli Pogostemon Patchouli - Calms and relaxes the mind by reducing the sympathetic nervous system activity. (Haze et al.)
Lavender Lavendula Angustifolia - It was found that inhalation of lavender oil vapor or linalool vapor may result in a decrease in the ACTH levels. This suggests that the inhalation of lavender or linalool vapor may be applied to relieve tension. 
Improving quality of sleep is the first line of defense when trying to maintain healthy homeostasis in the body is to encourage healthy sleep patterns. Sleep is necessary for both animals and humans throughout their life span. Insufficient sleep could result in adverse illnesses. Sleep deprivation or poor quality of sleep might promote obesity and diabetes, or it could aggravate the existing endocrine conditions. The primary symptom of menopause is insomnia, which is linked to decreased levels of estrogen and melatonin. Many studies point to the positive effects essential oils and their constituents have on the quality of sleep. One study demonstrated that inhalation of essential oils containing santalol, linalool, and cedrol improved the quality of sleep. Therefore, we can conclude oils such, Australian sandalwood, Ho wood or cedar oils can be complement in sleep formulations.